# Re: Value

From: JOG <jog_at_cs.nott.ac.uk>
Date: Sun, 24 Feb 2008 12:32:35 -0800 (PST)

On Feb 24, 3:26 pm, r..._at_zedat.fu-berlin.de (Stefan Ram) wrote:
> r..._at_zedat.fu-berlin.de (Stefan Ram) writes:
> >This notion is so wide that it might help to explain,
> >what is /not/ a value.
>
> I still would like to write more about values, from yet
> another point of view. I hope that this time it will be the
> most fundamental point of view:
>
> Whenever humans communicate, they refer to entities of a
> universe of discourse. An entity is something that exists.

Date, Introduction to Databases, p421: "we cannot state with any precision exactly what an entity _is_".

I'm telling you now... back... away... from the definition.... ;)

>
> But what exists? This is given by an agreement of the parties.
> For example, when mathematicians talk about set theory, they
> might agree to use the ZF axioms. These axioms include the
> axiom »There is a set with no elements, called the empty set.«
> Thus, they agree upon the existence of the empty set for this
> discourse.
>
> A complete model contains entities and also assertions about
> those entities, but it are those entities that are also being
> referred to as »values«.
>
> In computer programming there are two models of importance:
> The source code model and the run-time model.
>
> .----------------------------------------------------------.
> | Usually, those entities of the run-time model are called |
> | »values« that can be refered to by expressions of the |
> | source-code model. |
> '----------------------------------------------------------'
>
> Sometimes, these values also are known as »first-class values«.
>
> For example, in BASIC functions are not first-class values:
> They are part of the source-code model (DEF FNA(X)=...), but
> not of the run-time model (»FNA« is not an expression for FNA
> whose value can be assigned to another name nor are there
> function literals). In Scheme, functions are first-class values:
> There are function literals; and functions can be assigned
> to a name.
Received on Sun Feb 24 2008 - 21:32:35 CET

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